Suppression of C/EBPα expression in periportal hepatoblasts may stimulate biliary cell differentiation through increasedHnf6andHnf1bexpression

Abstract

The expression of C/EBP␣, which may govern transcription of mature hepatocyte marker genes, was suppressed in periportal hepatoblasts in mouse liver development, leading to biliary cell differentiation. This study was undertaken to analyze how inactivation of the Cebpa gene affects biliary cell differentiation and gene expression of the regulatory genes for that differentiation, including Hnf1b and Hnf6. In the knockout mouse liver at midgestation stages, pseudoglandular structures were abundantly induced in the parenchyma with elevated expression of Hnf6 and Hnf1b mRNAs. The wild-type liver parenchyma expressed mRNAs of these transcription factors at low levels, though periportal biliary progenitors had strong expression of them. These results suggest that expression of Hnf6 and Hnf1b is downstream of C/EBP␣ action in fetal liver development, and that the suppression of C/EBP␣ expression in periportal hepatoblasts may lead to expression of Hnf6 and Hnf1b mRNAs. Immunohistochemical studies with biliary cell markers in knockout livers demonstrated that differentiated biliary epithelial cells were confined to around the portal veins. The suppression of C/EBP␣ expression may result in upregulation of Hnf6 and Hnf1b gene expression, but be insufficient for biliary cell differentiation. When liver fragments of Cebpa-knockout fetuses, in which hepatoblasts were contained as an endodermal component, were transplanted in the testis of Scid (Prkdc) male mice, almost all hepatoblasts gave rise to biliary epithelial cells. Wild-type hepatoblasts constructed mature hepatic tissue accompanied by biliary cell differentiation. These results also demonstrate that the suppression of C/EBP␣ expression may stimulate biliary cell differentiation. Development 133, 4233-4243 (2006) DEVELOPMENT 4234 their up-or downstream relationships with the action of C/EBP␣ in biliary cell differentiation. The knockout mice are neonatal lethal because of hypoglycemia accompanied by hyperammonemia (Flodby et al., 1996; Kimura et al., 1998;Wang et al., 1995). Thus, it is intriguing to study what type of histology the knockout liver exhibits and how biliary epithelial tissue is induced when the knockouts survive. In vitro studies have demonstrated that knockout hepatocytes can immortalize at a higher frequency (Soriano et al., 1998). KEY WORDS: C/EBP␣ ␣, Knockout, Hepatoblasts, Biliary epithelial cells, Bile ducts, Morphogenesis, MouseIn the present study, we demonstrate the expression of biliary cell markers in pseudoglandular cells of Cebpa-knockout livers. Inactivation of the Cebpa gene not only suppresses hepatocyte maturation, but also upregulates regulatory genes for biliary cell differentiation such as Hnf6 and Hnf1b genes in the liver parenchyma, suggesting that the absence of C/EBP␣ in normal biliary cells induces Hnf6 and Hnf1b expression, leading to biliary cell differentiation. Jag1 and Notch2 mRNAs were also upregulated in knockout livers, but not to the same extent as Hnf6 and Hnf1b mRNAs. Testicular transplants of the knockout livers...

Transcription factor onecut3 regulates intrahepatic biliary development in zebrafish

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FGF signaling segregates biliary cell‐lineage from chick hepatoblasts cooperatively with BMP4 and ECM components in vitro

“…The onecut transcription factor Hnf6 and the downstream target, a homeodomain transcription factor Hnf1␤, have been shown to be expressed in mouse hepatoblasts and to regulate differentiation and morphogenesis of the bile duct system (Clotman et al, 2002;Coffinier et al, 2002). C/EBP␣, a liver-enriched transcription factor, is suppressed in mouse periportal hepatoblasts, and may control the high-level expression of Hnf6 and Hnf1␤ there (Yamasaki et al, 2006). In addition, Zebrafish vps33b, an ortholog of the gene responsible for human arthrogryposis-renal dysfunctioncholestasis syndrome, regulates biliary development downstream of Hnf6 (Matthews et al, 2006).…”

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